This invention relates a rotary fluid displacement apparatus, more particularly, to a fluid compressor or pump of the type which utilizes an orbiting piston member.
There are several types of fluid displacement apparatus which utilize an orbiting piston or fluid displacing member driven by a Scotch yoke type shaft coupled to an end surface of the piston or member. One apparatus, disclosed in U.S. Pat. No. 1,906,142 to John Ekelof, is a rotary machine provided with an annular, eccentrically movable piston adapted to act within an annular cylinder provided with a radial transverse wall. One end of wall of the cylinder is fixedly mounted and the other wall consists of a cover-disc connected to the annular piston, which is driven by a crank shaft. Other prior art apparatus are shown in U.S. Pat. Nos. 801,182 and 3,560,119. Though the present invention applies to either type of fluid displacement apparatus, i.e., using either an annular piston or scroll-type piston, description will be limited to the scroll type compressor. The term piston is used generically to describe a movable member of any suitable configuration, within a fluid displacement apparatus.
U.S. Pat. No. 801,182 discloses a scroll type apparatus including two scroll members each having a circular end plate and a spiroidal or involute spiral element. The scroll members are maintained angularly and radially offset so that both spiral elements interfit at a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of these scroll members shifts the line contact along the spiral curved surfaces and, therefore, changes the volume in the fluid pockets. The volume of the fluid pockets increases or decreases dependent on the direction of the orbital motion. Therefore, the scroll type fluid displacement apparatus is applicable to compress, expand or pump fluids. In comparison with conventional compressors of the piston type, a scroll type compressor has certain advantages such as fewer number of parts and continuous compression of fluid. However, there have been several problems, primarily sealing of the fluid pocket, wearing of the spiral elements, and outlet and inlet porting.
Although various improvements in the scroll type fluid displacement apparatus have been disclosed in many patents, for example, U.S. Pat. Nos. 3,884,599, 3,994,633, 3,664,635, and 3,944,636, such improvements have not sufficiently resolved these and other problems.
In particular, it is desired that sealing force at the line contact be sufficiently maintained in a scroll type fluid displacement apparatus, because the fluid pockets are defined by the line contacts between two spiral elements which are interfitted together, and the line contacts shift along the surface of the spiral elements by the orbital motion of scroll member, to thereby move the fluid pockets to the center of the spiral elements with consequent reduction of volume, and compression of the fluid in the pockets. On the other hand, if contact force between the spiral element becomes too large in maintaining the sealing of line contact, wear of spiral element surface increases. In view of this, contact force of both spiral elements must be suitably maintained. However, these contact forces can not be precisely maintained because of dimensional errors in manufacturing of the spiral elements. To decrease dimensional errors of spiral elements during manufacture, would unduly complicate the manufacture of the spiral elements.
The problem of sealing the fluid pockets is not completely resolved by the above mentioned patents.